Microsomal flavin-containing monooxygenases

Poulsen LL. 1981. Organic sulfur substrates for the microsomal flavin-containing monooxygenase. Rev Biochem Toxicol 3 33-49. 

This enzyme [EC 1.14.13.8], also referred to as microsomal flavin-containing monooxygenase and dimethyl-... 

Microsomal flavin-containing monooxygenases. As well as the cytochromes P-450 MFO system, there is also a system, which uses FAD. This flavin-containing monooxygenase or FMO enzyme system is found particularly in the microsomal fraction of the liver, and the monomer has a molecular weight of around 65,000. Each monomer has one molecule of FAD associated with it. The enzyme may accept electrons from either NADPH or NADH although the former is the preferred cofactor. It also requires molecular oxygen, and the overall reaction is as written for cytochromes P-450 ... 

Tertiary amines such as trimethylamine and dimethylamine had long been known to be metabolized to A -oxides by a microsomal amine oxidase that was not dependent on CYP. This enzyme, now known as the microsomal flavin-containing monooxygenase (FMO), is also dependent on NADPH and 02, and has been purified to homogeneity from a number of species. Isolation and characterization of the enzyme from liver and lung samples provided evidence of clearly distinct physicochemical properties and substrate specificities suggesting the presence of at least two different isoforms. Subsequent studies have verified the presence of multiple forms of the enzyme. 

Jones KC, Ballou DP. Reactions of the 4a-hydroperoxide of liver microsomal flavin-containing monooxygenase with nucleophilic and electrophilic substrates. J. Biol. Chem. 1986 261 2553-2559. 

This pathway accounts for the thiomethyl metabolites formed from several classes of xenobiotics. Thiomethyl metabolites can be further oxidized by the microsomal flavin-containing monooxygenases to their corresponding sulfoxide and sulfone derivatives. 

Hamman MA, Haehner-Daniels BD, Wrighton SA, et al. Stereoselective sulfoxidation of sulin-dac sulfide by flavin-containing monooxygenases. Comparison of human liver and kidney microsomes and mammalian enzymes. Biochem Pharmacol 2000 60(1) 7-17. 

Rettie, A., Bogucki, B., Lim, I. and Meier, P. (1990). Steroselective sulfadioxidation of a series of alkyl P-tolyl sulfides hy microsomal and purified flavin-containing monooxygenases. Mol. Pharmacol. 37 643-651. 

Tynes RE, Hodgson E. 1985. Magnitude of involvement of the mammalian flavin-containing monooxygenase in the microsomal oxidation of pesticides. J Agric Food Chem 33 471-479. 

Using pig and human microsomes and cDNA-expressed human flavin-containing monooxygenase, Lin and Cashman demonstrated a metabolic detoxification pathway that converts tyramine into the HA derivative, 20, and the anti oxime, 21, which was sufficiently stable to permit its chemical characterization". ... 

Monooxygenations are those oxidations in which one atom of molecular oxygen is reduced to water while the other is incorporated into the substrate. Microsomal monooxygenation reactions are catalyzed by nonspecific enzymes such as the flavin-containing monooxygenases (FMOs) or the multienzyme system that has cytochrome P450s (CYPs) as the terminal oxidases. 

Flavin containing monooxygenase Microsomal Oxidation NADPH 1 [89] ... 

A-demethylation of 1,1-dimethylhydrazine by rat and hamster liver microsomes in vitro required the presence of NADPH and oxygen and was decreased by the addition of flavin-containing monooxygenase inhibitor (methimazole) but not by the addition of cytochrome P-450 inhibitors (Prough et al. 1981). 

Several studies have shown that the reactive binding species generated by 1,1-dimethylhydrazine metabolism may be free radical intermediates. Rat liver microsomes and rat hepatocytes are capable of metabolizing 1,1-dimethylhydrazine to form methyl radical intermediates (Albano et al. 1989 Tomasi et al. 1987). The formation of tliese radicals was inhibited by the addition of inhibitors of cytochrome P-450 (SKF 525A, metyrapone, and carbon monoxide) and inhibitors of the flavin-containing monooxygenase system (methimazole). The formation of free radicals could also be supported nonenzymatically by the presence of copper ion (Tomasi et al. 1987). These data indicate that at least two independent enzyme systems and one nonenzymatic pathway may be involved in the metabolism of... 

Hormonal regulation of rat liver microsomal enzymes. Role of gonadal steroids in programming, maintenance, and suppression of delta 4-steroid 5 alpha-reductase, flavin-containing monooxygenase, and sex-specific c3ftochromes P-450. J. Biol. Chem. 261, 10728-10735. 

Buronfosse, T, Moroni, R, Benoit, E., and Riviere, J. L. (1995), Stereoselective sulfoxidation of the pesticide methiocarb by flavin-containing monooxygenase and cytochrome P450-dependent monooxygenases of rat liver microsomes. Anticholinesterase activity of the two sulfoxide enantiomer. J. Biochem. Toxicol. 10, 179-189. 

Tynes, R. E, and Hodgson. E. (1985). Catalytic activity and. substrate specificity of the flavin-containing monooxygenase in microsomal systems Characterization of the hepatic, pulmonary and renal enzymes of the mouse, rabbit, and rat. Arch. Biochem. Biaphys. 240,77-93. 

Teyssier C, Guenot E, Suschetet M, Siess MIT. Metabolism of diallyl disulfide by human liver microsomal cytochromes P-450 and flavin-containing monooxygenases. Drug Metab Dispos 1999 27 835-841. 

Wang et al. (2001) investigated the effect of salinity of water on the toxicity of aldicarb in fishes. Their stndies indicated that salinity-mediated enhancement of aldicarb toxicity was species-dependent. In rainbow tront, salinity increased the toxicity of aldicarb, the effect attribnted to greater sulfoxidation to aldicarb snlfoxide cansed by increased flavin-containing monooxygenase and the catalytic activities in microsomes of liver, gill and kidney of rainbow trout. 

Fisher MB, Yoon K, Vaughn ML, Strelevitz TJ, Foti RS. Flavin-containing monooxygenase activity in hepatocytes and microsomes in vitro characterization and in vivo scaling of benzydamine clearance. Drug Metab Dispos 2002 30 1087-1093. 

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